FLORAL MANIPULATION BY LASIOGLOSSUM ZEPHYRUM (HYMENOPTERA: HALICTIDAE) ENSURES FIRST ACCESS TO FLORAL REWARDS BY INITIATING PREMATURE ANTHESIS OF XYRIS TENNESSEENSIS (XYRIDACEAE) FLOWERS

Abstract

early bird gets the worm, is a cliche that often comes to mind when considering cases of exploitative competition in nature. In order to gain first access to pollen in flowers, some bees have been observed to chew holes in unopened flowers and poricidal anthers (Renner 1983; Young 1983; Hurd & Linsley 1963). Here we describe an interesting case of a bee, Lasioglossum zephyrum (Smith), manipulating a flower to open prematurely, thus ensuring first access to the floral rewards of Xyris tenneseensis Kral. Xyris tenneseensis is federally listed as endangered (U.S. Fish and Wildlife Service, 1994), and is only known from 14 extant populations. Our observations are restricted to a large population of X. tenneseensis located along the edge of a springfed pond in Fort McClellan, AL.Xyris tenneseensis is perennial, producing one flower (rarely two) per day from a cone-like inflorescence. The flower bud emerges from the inflorescence (Fig. la) approximately 45 minutes prior to natural anthesis. At this time a translucent membranaceous sepal sheaths the entire flower bud. As the bud continues to emerge, the flower petals exert outward pressure on the sheath-like sepal. This outward pressure on the sheath-like sepal causes it to slide up the flower bud and form an air-filled membranaceous atop the bud (Fig. 2b). Eventually the pressure exerted by the petals causes the sheath to fall off the flower, allowing the flower to open. The flower stays open for a few hours after which the corolla closes and falls off the inflorescence. Xyris tenneseensis flowers produce no nectar and anther dehiscence precedes anthesis. Previous studies indicate that the first visitor to a flower often gets a disproportionate amount of available floral resources (Harder 1990; Buchmann & Cane 1989). Due to the pre-anthesis presentation of pollen within the flowers of X. tenneseensis, the first floral visitor has access to all the floral rewards. Individuals of L. zephyrum (Fig. 2c) were seen to land on X. tenneseensis flower buds during the bubble stage (Fig. 2b). The bee would nip at the using its mandi-